1. Field of the Invention
The present invention relates to a pressure-sensitive amplifier stage comprising a modified Wheatstone bridge.
2. Description of the Prior Art
It is known to connect micromechanical pressure sensors in the manner of a Wheatstone bridge by connection of MOS transistors. Such bridge circuits are described e.g. in EP-A-0006740, EP-B-1 152 232 (DE-T-699 17 943), U.S. Pat. Nos. 4,275,406, 4,459,856, 4,522,072, DE-C-43 11 298, DE-A-44 44 808 and DE-U-78 28 255.
When using MOS transistors as pressure sensors in micromechanical sensors, it is usually necessary to combine the output signals of a plurality of such pressure sensors connected in the manner of a Wheatstone bridge, e.g. in order to reduce or suppress the influences of casing-related mechanical tension onto the measurement amount. For this purpose, the individual pressure sensors connected in the manner of a Wheatstone bridge are usually connected in a combination of row circuits and parallel circuits. This combination of the output signals of a plurality of Wheatstone bridges is effected in that, depending on the desired polarity, bridges will be switched into a parallel or antiparallel configuration. These arrangements have the disadvantage that the total useful signal of the combination of the plurality of said Wheatstone bridges is not stronger than the useful signal of an individual pressure sensor or an individual Wheatstone bridge. Thus, in other words, there occurs an averaging of the signal strengths and not an addition, while the latter would be desirable.
It is an object of the invention to provide a pressure-sensitive amplifier stage which is cascadable.